Mobile communication system and communication method

ABSTRACT

A mobile communication system which can transfer information on the number of packets counted up until then by a base station of a mobile source, to a base station of a mobile target, even when a terminal performs a handover. UE moves to a Target eNode B, but a Source eNode B decides to perform a handover, and the Source eNode B includes information on the number of packets counted up until then in a Handover Request message to the Target eNode B, so as to notify the Target eNode B. After receiving a Handover Confirm message from the UE, the Target eNode B includes information on the number of packets received from the Source eNode B in a Handover Complete message transmitted to a CN Node, so as to notify the CN Node.

The present application is a Divisional Application of U.S. patentapplication Ser. No. 14/798,663 filed on Jul. 14, 2015, which is aDivisional application Ser. No. 12/531,900 filed on Sep. 18, 2009, whichis a National Stage Entry of international applicationPCT/JP2008/055274, filed Mar. 21, 2008, which claims the benefit ofpriority from Japanese Patent Application 2007-074554 filed on Mar. 22,2007, the disclosures of all of which are incorporated in their entiretyby reference herein.

FIELD OF THE INVENTION

The present invention relates to a mobile communication system and basestation thereof, and in particular to information relating to the numberof packets (namely, data volume) at handover in the mobile communicationsystem.

BACKGROUND OF THE INVENTION

A mobile communication system in 3GPP (3rd Generation PartnershipProject) LTE (Long Term Evolution) aims for an architecture as shown inFIG. 7. It is an object of this architecture to build a system that canrealize shortening of transmission delay in a control plane and a userplane, and in which data transfer with higher throughput, for example,than existing systems can be realized.

An operator provides a service to a user in this system, and charges afee; one charging method therefor that can be considered is to chargeonly for the number of packets that the user used.

In order to charge for the number of packets that the user used, it isnecessary to count the number of packets that the user used. A method ofdoing this count is to count only the amount of packets that a networkhas successfully received, in an uplink case, and to count only theamount of packets that a user has successfully received, in a downlinkcase, and to charge for the number of counted uplink and downlinkpackets only.

With regard to counting the number of packets, since the number ofpackets successfully received is counted in the uplink case, normally CN(Core Network) Nodes of the network perform the count.

In the downlink case, packets transmitted by the network are notnecessarily completely delivered to UE (User Equipment), due to radiowave state. For example, packet #1, packet #2, and packet #3 aretransmitted from a network to the UE; packet #1 and packet #2 aresuccessfully received by the UE, but packet #3 is not successfullyreceived by the UE. In view of this type of situation, counting theamount of packets successfully received is considered at the UE. Thatis, counting is performed by a self-assessment of the UE.

However, if the UE performs the count, a case may be considered where,for example, a malicious UE or an altered UE reports to the network anumber less than the actual number successfully received. In order toprevent this, the number of downlink packets is usually counted by thenetwork. In this mechanism, for downlink packets transmitted from thenetwork to the UE, a confirmation is made that a transmissionconfirmation (Acknowledge) from the UE has been received by the network,and the number of downlink packets is counted.

A function of this transmission confirmation is held by an entity calledRLC (Radio Link Control) at an eNode B of the network, so that thenumber of successfully transmitted downlink packets is counted by theeNode B. This situation is shown in FIG. 9. Furthermore, “reporting thenumber counted to a CN Node”, which reports to the CN Node, from theeNode B shown in FIG. 9, is normally performed when communicationbetween the eNode B and the UE is ended and communication connection iscut.

On the other hand, in this LTE architecture, when an area covering oneeNode B is small (for example, an urban area), there is a possibilitythat handover signals from the eNode B to the CN Node will increaseenormously, due to UE movement between eNode Bs. In such a case, anexcessive signal load is given to the CN.

In order to suppress handover signal load on the CN Node, exchanging ofhandover signals directly between a mobile source base station (SourceeNode B) and a mobile target base station (Target eNode B) is devised.Furthermore, with a handover signal (Handover Request message of FIG. 8)received by the Target eNode B from the Source eNode B, if the handoveris successful, that is, if confirmation of the Target eNode Bestablishing a communication connection with the UE is completed, thehandover procedure is completed by the Target eNode B only transmittingone Handover Complete signal to the CN Node.

Here, the Handover Complete signal name is an example, and there areother names such as, for example, Path Switch, Binding Update, and thelike, all of which have the same meaning.

The CN Node that receives this Handover Complete signal switches a UEdirected path from the Source eNode B to the Target eNode B. In thisway, it is possible to reduce the signal load and processing load due tohandover at the CN Node.

In this handover method, information on the number of downlink packetscounted before the mobile source eNode B performs handover, that is,“reporting the number counted to the CN Node” of FIG. 9 must be reportedto the CN Node. Otherwise, the number of packets counted by the mobilesource eNode B cannot be charged for.

In a conventional handover method (shown in FIG. 10), with a disconnectsignal (Iu Release Command) from the CN Node as a trigger, the numbercounted by the mobile source eNode B is reported to the CN Node by themobile source eNode B. Specifically, the Source eNode B reports thecounting method to the CN Node by an Iu Release Complete message of FIG.10.

Furthermore, even outside of the handover case, after ending ofcommunication between the UE and the network, similarly to the above,with a disconnect signal (Iu Release Command) from the CN Node as atrigger, the eNode B reports the method of “reporting the number countedto the CN Node” to the CN Node by the Iu Release Complete message.

Technology related to the abovementioned mobile communication system isdisclosed in the following patent documents.

[Patent Document 1]

JP Patent Kokai Publication No. JP-P2003-283510A

[Patent Document 2]

JP Patent Kokai Publication No. JP-P2007-013463A

[Patent Document3]

JP Patent Kohyo Publication No. JP-P2001-513285A

SUMMARY

The entire disclosure of Patent Documents 1 to 3 is incorporated hereinby reference thereto. An analysis of related technology according to thepresent invention is given below.

With regard to this LTE handover method, since a disconnect signal froma CN Node to a Source eNode B does not exist, there is a problem in thatthe amount counted by the Source eNode B cannot be reported to the CNNode.

This problem causes a further problem in that, since the Source eNode Bcannot report the number of packets successfully received before a UEhandover to the CN Node, it is not possible to accurately charge for thenumber of packets successfully received before the UE handover.

Consequently, it is an object of the present invention to solve theabovementioned problems, and to provide a mobile communication system(and in particular, a base station therefor) in which information on thenumber of packets (that is, data volume) counted up to now at a basestation of a mobile source can be transferred to a base station of amobile target even when a terminal performs a handover.

A mobile communication system according to the present invention is amobile communication system for transmitting downlink packets from abase station to a terminal, and includes the number of downlink packetsin Data Volume Information from the base station.

That is, in the mobile communication system of the present invention,accompanying movement (handover) of a terminal (UE: user equipment) froman area of a mobile source base station (Source eNode B) to an area of amobile target base station (Target eNode B), the mobile source basestation transfers information on the number of packets communicated tothe terminal before movement, to the mobile target base station, and themobile target base station provides notification including informationon the number of the packets in question in a message reporting handovercompletion (Handover Complete) to a CN Node (Core Network; or alsoreferred to as EPC (Evolved Packet Core)).

Accompanying movement of the terminal from the area of the mobile sourcebase station to the area of the mobile target base station, the mobilesource base station provides, with regard to information on the numberof packets communicated up until the terminal moves, notificationincluding information on the number of the packets in question in amessage (Release Resource Indication) reporting handover completion tothe CN Node; and at a time of switching of the CN Node due to handover,provides notification of the number of packets of the UE stored by aswitching source CN Node, to a switching target CN Node.

In this way, in the mobile communication system of the presentinvention, it is possible for information on the number of packetscounted up until then by the eNode B to be transferred to the TargeteNode B where the UE is moving to, even if the UE is undergoing handoverbetween eNode Bs. That is, in the mobile communication system of thepresent invention, for example, after termination of UE communication,it becomes possible to accurately report the number of packets countedby the eNode B to the CN Node, and since the CN Node can report to acharging center, it becomes possible to have accurate charging.

Furthermore, in the mobile communication system of the presentinvention, even if the CN Node is switched due to a handover, byproviding notification of information of the number of packets countedup until then from the switching source CN Node to a switching target,since it is possible to report information on the number of communicatedpackets of the UE to the charging center, it becomes possible to haveaccurate charging.

Various Aspects of the Invention are Described Below.

In a first aspect of the present invention, there is provided a basestation for communicating with a wireless terminal. The base station hastransmission means for transmitting information related to data volumeof downlink data to a second base station, when the wireless terminalperforms a handover from the base station to the second base station.(Basic Mode 1)In a second aspect of the present invention, there is provided awireless communication system having a first base station, a second basestation, and a wireless terminal. The wireless terminal performshandover from the first base station to the second base station; thefirst base station, when the handover is performed, transmitsinformation related to the data volume of downlink data to the secondbase station; and the second base station receives the informationrelated to the data volume.In a third aspect of the present invention, there is provided acommunication method of a base station with regard to a wirelessterminal. That is, the method is characterized by including a process ofthe wireless terminal performing a handover from a base station to asecond base station, and a process of transmitting information relatedto the data volume of the downlink data, when the handover is performed,to the second base station.In a fourth aspect of the present invention, there is provided acommunication method of a wireless communication system having a firstbase station, a second base station and a wireless terminal. That is,the method is characterized by including a process of the wirelessterminal performing a handover from the first base station to the secondbase station, a process of the first base station transmittinginformation related to the data volume of the downlink data, when thehandover is performed, to the second base station, and a process of thesecond base station receiving information related to the data volume.

In the present invention, by the abovementioned configuration andoperation, an effect is obtained in which, even when a terminal performsa handover, it is possible for information on the number of packetscounted up until then at a base station of a mobile source to betransferred to a base station of a mobile target.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sequence chart showing a handover procedure of a mobilecommunication system according to a first exemplary embodiment of thepresent invention.

FIG. 2 is a sequence chart showing a procedure of reporting informationcounted according to the first exemplary embodiment of the presentinvention.

FIG. 3 is a drawing showing information (data volume report) of thenumber of packets reported in the first exemplary embodiment of thepresent invention.

FIG. 4 is a sequence chart showing a handover procedure of a mobilecommunication system according to a second exemplary embodiment of thepresent invention.

FIG. 5 is a sequence chart showing a procedure of reporting informationcounted according to a third exemplary embodiment of the presentinvention.

FIG. 6 is a sequence chart showing a procedure of transferring countinformation between CN Nodes according to a fifth exemplary embodimentof the present invention.

FIG. 7 is a drawing showing a conventional LTE network configuration.

FIG. 8 is a sequence chart showing a conventional handover procedure.

FIG. 9 is a sequence chart showing a conventional procedure of countingthe number of packets and reporting.

FIG. 10 is a sequence chart showing a procedure of reporting the numberof packets counted at a mobile source eNode B in a conventional handovermethod.

PREFERRED MODES

As expanded embodiments of the present invention, configurationsdescribed in each dependent claim are specified. Downlink data ispreferably data transmitted from a (first) base station to a wirelessterminal. (Mode 2)

Downlink data is preferably data successfully transmitted from the(first) base station to the wireless terminal. (Mode 3)

Information related to data volume preferably includes time informationon a time period in which the downlink data is transmitted. (Mode 4)

A transmission means preferably transmits information related to thedata volume by a message requesting a handover. (Mode 5)

There is preferably a second transmission means for transmitting amessage indicating completion of resource release from the (first) basestation to a second base station, and the second transmission meanspreferably transmits information related to the data volume includingthe message indicating completion of resource release, before handover.(Mode 6)

After communication with the wireless terminal has been completed, theinformation related to the data volume is preferably transmitted to acore network in a message indicating completion of resource release.(Mode 7)

Information related to the data volume is preferably information on thenumber of downlink data packets. (Mode 8)

The second base station preferably transmits information related to thedata volume by a message that completes handover to the core network.(Mode 9)

The first base station preferably includes and transmits to the secondbase station information related to the data volume in the messageindicating the resource release. (Mode 10)

After communication between the first base station and the wirelessterminal has been completed, information related to the data volume ispreferably transmitted to the core network in a message indicating thatthe resource release is completed. (Mode 11)

The second base station preferably transmits information related to datavolume by a message that reports handover completion to the corenetwork. (Mode 12)

After transmission of a message requesting context information of a UE,to a first core network communicating with the first base station, froma second core network communicating with the second base station, thefirst core network preferably includes information related to datavolume of uplink and downlink data summed up until then, in a messageresponding to the message requesting the context information of the UE,and transmits to the second core network. (Mode 13)

Next, a description of exemplary embodiments of the present invention isgiven making reference to the drawings.

EXEMPLARY EMBODIMENT 1

FIG. 1 is a sequence chart showing a handover procedure of a mobilecommunication system according to a first exemplary embodiment of thepresent invention; FIG. 2 is a sequence chart showing a procedure ofreporting information counted according to the first exemplaryembodiment of the invention; and FIG. 3 is a drawing showing information(data volume report) of the number of packets reported in the firstexemplary embodiment of the present invention. Making reference to FIGS.1 to 3, a description is given concerning operation of the mobilecommunication system according to the first exemplary embodiment of thepresent invention.

In the description below, the mobile communication system according tothe first exemplary embodiment of the present invention is configuredfrom the respective devices:

Source eNode B=mobile source base station

Target eNode B=mobile target base station

UE (User Equipment)=wireless terminal, also referred to simply asterminal, and

CN=Core Network, also referred to as ASGW (Access Gateway) or AccessAnchor, but CN is a general term thereof, and there is no limitationthereto.

In FIG. 1, the UE is communicating with a Source eNode B. The UE movesto a Target eNode B, but the Source eNode B decides to perform ahandover, and the Source eNode B includes information on the number ofpackets counted up until then (the number of packets received by the UE)in a Handover Request message to the Target eNode B, to notify theTarget eNode B.

After the Target eNode B receives a Handover Confirm message from theUE, information on the number of packets counted, that has been receivedfrom the Source eNode B, is included in a Handover Complete messagetransmitted to the CN Node, and transmitted to the CN Node. Based on theinformation on the number of counted packets transmitted from the TargeteNode B, the CN Node sums the number stored up until then, and storesthis in memory.

This method can be described as in “The eNode B shall report to the CNin the Handover Complete message the data volume information if receivedfrom other eNode B during the handover procedure”, or “The eNode B ifhas stored the data volume information from other eNode B, shall reportto the CN in the Handover Complete message the data volume information”.

Furthermore, timing of reporting the number of packets counted from theeNode B to the CN Node, as shown in FIG. 2, accompanying UEcommunication completion, for example, in order to release a resource tothe eNode B, the CN Node transmits an S1 Context Release Request, andthe eNode B replies to the CN Node with an S1 Context Release Completemessage after completion of resource release, but with this S1 ContextRelease Complete message, a CN Node report may be performed, summing thenumber of packets counted that have been received from other eNodes B bythe handover up until then and the number of self-counted packets.

The CN Node reports information (downlink) on the number of packetscounted that have been received from the eNode B and information(uplink) on the number of self-counted packets to the charging center.

The information on the number of packets counted, transmitted from theSource eNode B, may be the number successfully transmitted to the UE,but may also be the number unsuccessfully transmitted to the UE. In acase where the information on the number of packets counted is taken asthe information on the number unsuccessfully transmitted, for the CNNode the number successfully transmitted is the number of packetstransmitted by the CN Node less the number unsuccessfully transmitted.This is expressed by a formula:

number of successfully transmitted packets=number of packetstransmitted−number of packets unsuccessfully transmitted.

The information on the number of packets shown in FIG. 3 isUnsuccessfully Transmitted DL Data Volume, that is, number of packetsunsuccessfully transmitted, but this may be Successfully Transmitted DLData Volume, that is, the number successfully transmitted.

In this way, in the present exemplary embodiment, even with a handoverof the UE between the Source eNode B and the Target eNode B, theinformation on the number of packets counted up until then by the SourceeNode B can be transferred to the Target eNode B where the UE is movingto. In the present exemplary embodiment, for example, after terminationof UE communication, it is possible to accurately report the number ofpackets counted by the eNode B to the CN Node, and since the CN Node canreport to a charging center, it is possible to have accurate charging.

EXEMPLARY EMBODIMENT 2

FIG. 4 is a sequence chart showing a handover procedure of the mobilecommunication system according to a second exemplary embodiment of thepresent invention. With regard to FIG. 4, in the present exemplaryembodiment, a Release Resource Complete message is provided from aSource eNode B to a Target eNode B, and information on the number ofpackets counted by the Source eNode B before handover is included in theRelease Resource Complete message and transmitted.

In the present exemplary embodiment, for example, in a case where thehandover procedure has been unsuccessful due to the Target eNode Bfailing to capture a resource or the like, it is possible to eliminateneedless information transfer by a handover request message from theSource eNode B.

Furthermore, timing of reporting the number of packets counted from theeNode B to the CN Node, as shown in FIG. 2, for example, accompanying UEcommunication completion, in order to release a resource to the eNode B,the CN Node transmits an S1 Context Release Request message, and theeNode B replies to the CN Node with an S1 Context Release Completemessage after completion of resource release, but with this S1 ContextRelease Complete message, a report is made to the CN Node, summing thenumber of packets counted that have been received from other eNodes Bdue to the handover up until then, and the number of self-countedpackets.

The CN Node reports information (downlink) on the number of packetscounted that have been received from the eNode B, and information(uplink) on the number of self-counted packets, to a charging center.

In this way, in the present exemplary embodiment, even with handover ofthe UE between the eNode Bs, the information on the number of packetscounted up until then by an eNode B can be transferred to the CN Node,and since the CN Node can report to the charging center, it is possibleto have accurate charging.

EXEMPLARY EMBODIMENT 3

FIG. 5 is a sequence chart showing a procedure of reporting informationcounted according to a third exemplary embodiment of the presentinvention. Making reference to FIG. 5, a description is given of theprocedure of reporting information counted according to the thirdexemplary embodiment of the present invention.

As shown in FIG. 5, after carrying out a handover, if a Source eNode Breceives a Release Resource from a Target eNode B, information on thenumber of packets counted up until then is reported to a CN Node by aRelease Resource Indication message, and information on the number ofpackets thus counted is summed with the number of packets counted by theCN Node up until then, and stored in memory.

Thereafter, the CN Node reporting to a charging center involves, forexample, accompanying UE communication completion, in FIG. 2, reportingthe number of packets counted, which have been received up until then bythe CN Node, to the charging center.

In this way, in the present exemplary embodiment, even with the handoverof the UE between the eNode Bs, the information on the number of packetscounted up until then by an eNode B can be transferred to the CN Node,and since the CN Node can report to the charging center, it is possibleto have accurate charging.

EXEMPLARY EMBODIMENT 4

In the mobile communication system, packet charging may be differentaccording to time period. For example, a packet charge after 11 pm maybe set to be cheaper than the charge before 11 pm. In order to deal withthis, in the first exemplary embodiment of the present inventiondescribed above, it is possible to provide time period information ininformation on the number of packets counted that is notified by aSource eNode B to a Target eNode B. For example, time information may beprovided in a Data Volume Reference of FIG. 3.

EXEMPLARY EMBODIMENT 5

FIG. 6 is a sequence chart showing a procedure of transferring countinformation between CN Nodes according to a fifth exemplary embodimentof the present invention. With an LTE architecture as shown in FIG. 6,an eNode B of a UE mobile source may change CN Node, according tohandover.

For example, in a case where distance between an eNode B of a mobiletarget and a CN Node before moving is far, the eNode of the mobiletarget switches to a CN Node at a closer distance. Describing thisspecifically, in FIG. 6, with the UE communicating with eNode B #1 andthe CN Node #1, the UE moves to the eNode B #2, due to a handover, butsince the eNode B #2 and the CN Node #1 are at a distance that does notyet cause a problem, the CN Node #1 does not change.

Thereafter, the UE moves further to the eNode B #3, but since thedistance between the eNode B #3 and the CN Node #1 becomes large, theeNode B #3 switches to the CN Node #3. By the CN Node switchingaccording to this handover, for example, there is an effect related toshortening of transmission delay.

Since, in the switching of CN Node according to the handover, aswitching target CN Node does not have information on the number ofpackets communicated by the UE up until this, when communication of theUE is ended later, it is not possible to report accurate information,when reporting to the charging center.

In order to eliminate this problem, in the present exemplary embodiment,as shown in FIG. 6, Context information on the UE is requested of theswitching source CN Node #1 from the switching target CN Node #3 by aContext Request message, but the switching source CN Node #1 includesinformation on the number of uplink and downlink packets summed up untilthen, in the Context Response message, so as to notify the switchingtarget CN Node #3.

When the UE later ends communication, the CN Node #3, as shown in FIG.2, reports the number of packets counted, that have been received upuntil then, to the charging center.

In this way, in the present exemplary embodiment, even when the CN Nodeis switched according to the handover, by notifying information on thenumber of packets counted up until then, from the switching source CNNode to the switching target CN Node, since it is possible to reportinformation on the number of packets communicated by the UE to thecharging center, it is possible to have accurate charging.

The above operations are executed by a computer readable program, andclearly the base stations (first and second) and the communicationterminals are provided with storage devices for storing the program andcommunication data.

Modifications and adjustments of embodiments and examples are possiblewithin the bounds of the entire disclosure (including the scope of theclaims) of the present invention, and also based on fundamentaltechnological concepts thereof. Furthermore, a wide variety ofcombinations and selections of various disclosed elements are possiblewithin the scope of the claims of the present invention.

In the present invention, there are further possible modes as follows.

(Mode II-1) A communication method of a wireless communication systemhaving a first base station, a second base station, and a wirelessterminal, the method comprises: a process of the wireless terminalperforming a handover from the first base station to a second basestation; a process of the first base station transmitting informationrelated to data volume of downlink data to the second base station, whenthe handover is performed; and a process of the second base stationreceiving information related to the data volume.(Mode 11-2) In the communication method according to Mode II-1, thefirst base station transmits information related to the data volume by amessage requesting a handover.(Mode 11-3) In the communication method according to Mode II-1 or 11-2,the second base station transmits information related to the data volumeby a message completing a handover to a core network.(Mode 11-4) In communication method according to any one of Modes II-1to 11-3, the first base station includes information related to the datavolume in a message indicating completion of the resource release,before a handover, and transmits to the second base station.(Mode 11-5) In the communication method according to Mode II-1, aftercommunication between the first base station and the wireless terminalis completed, information related to the data volume is transmitted in amessage indicating completion of resource release to a core network.(Mode 11-6) In the communication method according to Mode II-1, thesecond base station transmits information related to the data volume ina message reporting handover completion to a core network.(Mode 11-7) In the communication method according to Mode II-1, aftertransmission of a message requesting context information of a UE, to afirst core network communicating with the first base station, from asecond core network communicating with the second base station, thefirst core network includes information related to data volume of uplinkand downlink data summed up until then, as information related to thedata volume, in a message responding to a message requesting contextinformation of a UE, and transmits to the second core network.

1. A method of communicating, the method comprising: transmitting, froma base station to a second base station, information that indicatesunsuccessfully transmitted downlink data volume, if a wireless terminalperforms a handover from the base station to the second base station;the second base station accumulating information indicating a datavolume for a report on a resource release; the second base stationreceiving, from a core network, a request message related to theresource release; and in response to the receiving the request message,the second base station transmitting, to the core network, a totalamount of the data volume.
 2. The method of claim 1, wherein thetransmitting from the base station to the second base station comprisestransmitting the information by a message relating to committing thehandover.
 3. A method of communicating, the method comprising:performing, by a wireless terminal, a handover from a first base stationto a second base station; transmitting, from the first base station tothe second base station, information that indicates unsuccessfullytransmitted downlink data volume; accumulating, by the second basestation, information indicating a data volume for a report on a resourcerelease; receiving, by the second base station, a request messagerelated to the resource release from a core network; and in response tothe receiving, transmitting, from the second base station to the corenetwork, a total amount of the data volume.
 4. The method according toclaim 3, wherein the transmitting, from the first base station,comprises transmitting the information by a message relating tocommitting the handover.
 5. A communication method in a communicationsystem including a first base station and a second base station, thecommunication method comprising: communicating, by the first basestation, with a wireless terminal; transmitting, by the first basestation to the second base station, information that indicatesunsuccessfully transmitted downlink data volume, if the wirelessterminal performs a handover from the first base station to the secondbase station; accumulating, by the second base station, informationindicating a data volume for a report on a resource release; andtransmitting, from the second base station to a core network, a totalamount of the data volume, when the second base station receives, fromthe core network, a request message related to the resource release. 6.The communication method according to claim 5, wherein the transmittingfrom the first base station to the second base station comprisestransmitting the information by a message relating to committing thehandover.
 7. A method of communicating by a base station, the methodcomprising: receiving from a second base station, information thatindicates unsuccessfully transmitted downlink data volume, if a wirelessterminal performs a handover from the second base station to the basestation; accumulating the information indicating a data volume for areport on a resource release; and transmitting, to a core network, atotal amount of the data volume when the base station receives, from thecore network, a request message related to the resource release.
 8. Themethod according to claim 7, wherein the receiving from the second basestation comprises receiving the information by a message relating tocommitting the handover.